Light-sensitive tube



G. R. sTlLwELL 1,942,501v

LIGHT SENS ITIVE TUBE Jan. 9, 1934.

Filed April 6, 1927 Afro/mfr diameter.

Patented Jam. 9, 1934 4 UNITED STATES 1,942,501 v LIGHT-SENSITIVE' TUBE George R. Stilwell, Bayonne, N. J., assigner to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application April 6, 1927. Serial No. 181,552

12 Claims.

1'1/2 inches in diameter. For a disclosure of this.

type of tube the reader is referred to an article entitled, The alkali metal photoelectric cell by Herbert E. Ives in the Bell System Technical Journal, Volume V, April, 1926.

When an attempt was made by the present inventor to increase the size of light-sensitive tubes of the type just mentioned for the purpose of increasing their sensitivity. it was found impossible to obtain a continuous opaque coating by distillation such as had been obtained in the small tubes.

The present invention is the outgrowth of a research into the causes of this failure and the practicability of obtaining large light-sensitive tubes. It pertains both to the method of obtaining a coating of light-sensitive material' and to the structure of light-sensitive tubes, and although particularly applicable to tubes of large size, is applicable also 1o tubes of small size.

In accordance with the invention the deposit of light-sensitive material is obtained by providing a specially or critically positioned auxiliary member or surface Within the tube and rst obtaining a deposit thereupon, which deposit is later revaporized and redeposited upon the inner surface of the outer walls of the tube. The preferred form of tube is cylindrical in shape, a foot or more in length and at least several inches in The auxiliary member takes the form of a reentrant tubular stem extending along the major axis of the cylinder, closed at the end projecting within the tube and open at the other end to receive either a heating element or a cooling medium. The anode is in the form of a wire helix surrounding the reentrant stem and held firmly in place thereby, so as to prevent it from vibrating either as a whole or in segments. The reentrant stern is transparent and'of small diameter so as to offer little obslruction to incident light when the tube is in use. The tube window, which preferably extends the full length of, and half way around the tube, is produced by applying a moderate amount of heat to lone side of the outer wall by flaming it with a point flame so as to cause the light-sensitive coating to flow back upon itself without being vaporized.

The following is a deLailed description of the preferred form of the invention. prefaced by a brief description of the method heretofore used.

Fig. l of the drawing illustrates the arrangement for the preliminary step in the formation of the light-sensitive coating in the tube accord' ingv to the invention.

Fig. 2 shows the arrangement 0i' apparatus for` 65 the final step of transferring the coating to the inside surface of the outer wall of the tube.

Fig. 3 illustrates a light-sensitive tube made in accordance With the invention with a portion broken away to show the detailed construction.

Heretofore it has been the practice to obtain the coating of light-sensitive material in the tube by connecting the bulb, which is to form the tube, to a vacuum pump and also to a container of vapor of the light-sensitive substance. The vapor is produced in this container, which contains a supply of the light-sensitive material, by the application of heat thereto. Meanwhile the walls of the tube are maintained at room temperature, which is below the solidfying temperature ofthe vapor. The pressure is maintained so low that the mean free path of the molecules is large compared with the size of the tube, so that the vapor entering the tube .continues to move in the direction in which it enters until it strikes the wall opposite the entrance, where a large part of it is deposited by being condensed and solidified. The vapor entrance is then closed and a heating medium is substituted for the cooling medium upon the portion of the tube wall Which carries the deposit, the other portion of the tube wall upon which it is desired to have a coating being meanwhile kept cold. The heating is ordinarily accomplished with a flame which is applied upon and around the spot where the depositie formed until the latter has been revaporized and recondensed where desired. If a deposit occurs elsewhere in the tube where it is not wanted the flame is applied to that portion in the same manner- The tubes heretofore made have been small, as stated above. It was desired to'increase the sensitivity of such tubes by making them many times larger, with the idea of thus bringing practical television one step nearer. Consideration was then given to the form a large tube should take.

It was decided that cylindrical tubes several inches in diameter and with a length several times the diameter would not only be well suited for use in television systems but would be practical from/Thpoints of view of cost, ability to withstand atmospheric pressure, and ruggedness. However, when it was attempted to deposita coating of light-sensitive material upon the inner surface of the wall of such a tube by the usualv process it was found impossible to obtain a continuous opaque coating such as had been ob-v tained in the small'tubes. This failure seemed to be due to the sizeof the container or its tubu-A lar shape or both. It was subsequently discovered that when a specially positioned auxiliary member or surface is provided within the tube a deposit can readily be made upon it, which deposit can be revaporized and recondensed on the inner surface of the outer wall, and that the most vsuitable location for this auxiliary body or surface is along a major axis of the tube.

'I'he invention also utilizes the auxiliary member as a support for the anode when the member is so positioned that this can be done. l

The invention goes further than this in using a centrally located tubular member, preferably of transparent material, as a support for th'e anode whether or not' such member is also 'used for the purpose set forth above. It has been discovered that such anarrangement is a marked improvement over light-sensitive tubeshereto-v` .fore manufactured. :It does .away with vibrathe helix being short-circuited by the wire 13 intersectingthe turns. One end of the helix 12 is sealed through the enclosing vessel adjacent the hollow stem to form the leading-in wire for` the anode 12. A leading-in wire 14 is sealed into the cylindrical wall of the vessel 10, the-inner end of vwhich is bent to lie along the inner surface of the vessel. A continuous coating vof a light-sensitive material is formed on the inner surface of the vessel, by a method to be hereinafter described, and forms the light-sensitive electrode or cathode of the'photoelectric tube. This arrangement forms a light-sensitive tube of rigid construction in which distortion due to vibration of the central electrode is eliminated and the helical anode causes very little obstruction to incoming light rays. Furthermore, the capacitance of the tube is kept at a minimum.

Preparatory to lthe formation of the lightsensitive coating, the assembled tube structure is connected to a pumping system by the tubulation 15. A glass tube 16, preferably of pyrex glass, is connected to one side of the enclosing vessel 10 as shown in Fig. l. This tube is provided with a plurality of constricted portions 17 'to form a series of bulbs between a gas chamberA (not shown) and the interior of the vessel 10.

A larger bulb 18 intermediate the ends of the\ k tube 16 is connected to a receptacle 19 in which is placed a portion of glass tube 20 Acontaining a light-sensitive material, such as potassium, or other alkali metal. The potassium is previously purified and sealed in long glass tubes sel 10 in sumcient quantity to subsequently form sium is introduced into the receptacle 19 and sealed therein. The potassium is heated in the A receptacle 19 by any suitable means, as for inf stance, by a burner 21, to distill it into the bulb 18. The potassium deposited in the bulb 18 is then redistilled into the series of bulbs formed by the constricted portions 17 in the glass tube 16, to eliminate impurities,- in the usual manner. The potassium is then redistilled into the vessoA a continuous opaque coating on the inner surface of the vessel. The vessel 10 y'during this stage is maintained at room temperature, and a flame may be played'upon the walls where deposition isgreatest. fI-Iowever, the flaming may be postponed until after the vapor has been condensed. As the result of the condensing and naming, a deposit is formed on various portions of the tube walland the central stem andelecf trode 12, the greater amount being formed in a pool at the lower end of the tube. This-comf plete's the preliminary step in distilling the potassium into the tube 10.

A suitable coolingiluid, preferably liquid air, is poured into the hollow stem l1 and the cylindricalsurface ofthe tube 10 is heatedby suitable means, as by flaming, to vaporize the potassium on the inner surface of the tube. -The potassium vapor is condensed on the cooled surface of the stem 11 and the electrode 12. This 105 heating and cooling is continued until all the potassium isdeposited on the central stem and electrode. AvThe cooling nedium is then removed from the central stem 11 and the vessel and central stem are allowed to' return to room tempera- 110 ture. Fig. 2 shows the potassium coating 22' on the stem and electrode 12. After the tube has cooled to room temperature, a double walled receptacle 23 is placed around the vessel `10 and filled with a cooling liquid 24, such as liquid air.` A heater element 25 'is inserted in the hollow stem 1l, to vaporize the coating 22 on the. stemy 11 and electrode 12. The vapor Athen condenses on the cooled inner wall of the vessel 10 and this heating and cooling is continued until all the potassium is redistilled from the stem 11 and 'electrode 12 .and deposited on the inner wall of the vessel. The heater element 25 is then re- `moved from the hollow stem 11, and the vessel 23 containing the cooling medium is removed 125 from the outside of the vessel 10.

The next step is the removal of a portion -of the light-sensitive coating to form a window. In the 'manufacture of small tubes this has been accomplished by naming the surface ofthe vessel where it is desired to remove the coating, the heat being suflicient to vaporize all the coating which it is desired to remove. This vapor forms an additional coating on the remainder of the inner surface of the tube by condensation. This method is not suited, however, to the case in hand when a reentrant stem or auxiliary tubular memberof transparen r*material upon which an open-work anode is mounted, is employed. 'Ihis is for vthe reason that light from f the window passes through the transparent reentrant stem or tubular member thus preventing a shadow being cast and the sensitivity of the tubelowered. If the window were produced by vaporizing the light-sensitive material, an ji; opaque coating would be formed on' the walls of the stem, unless this element were maintained hot while thef window is being formed, which is inconvenient. Moreover, when the area and a portion of the tube containing the potasof the window islarge compared to the total area.

of the tube Wall it isdifflcult to maintain all of the window area at the desired high temperature and the remainder of the wall at the desired low temperature. The window must, of course, be made after the tube'has been removed from the liquid air bath.

To overcome these difficulties the following method has been evolved. 'I'he tube, which is in a vertical position on the pump to permit easy application of the liquid air bath, is changed-into a horizontal position by softening the neck of the supporting glass tube 15 and twisting the tube into the desired position. A point flame is then played upon the tube wall along a horizontal line near the top of the tube, this flame being allowed to remain in one place only long enough to melt the potassium without vaporizing it. rI'he melted potassium flows downward a short distance adhering to the tube wall and then solidies. The point flame is then played back and forth with a steady downward progression until the window is of the desired size. The potassium which has been melted during the process ultimately forms a ridge' or a coating of greater thickness along the bottom of the window. The window preferably extends nearly the full length of the tubeand half way around it.

The tube is then completed in a well known manner by subjecting the potassium coating to a glow discharge in an atmosphere of hydrogen, then replacing the hydrogen by an inert gas, such as argon, neon or helium, and subsequently sealing olf the tubulation l5 and distillation tube 16. The tube is then in the completed form as shown in Fig. 3.

By this method it is possible to construct photoelectric tubes having a light-sensitive opaque continuous coating over the full length of the tube and of relatively large size compared with the usual spherical type of photoelectric tube lhaving a diameter of approximately one and one-half inches. A typical tube made in accordance with this invention comprises a cylindrical enclosing vessel having a diameter of three and one-half inches anda length of fteen inches with a hollow tubular member three-eighths of an inch in diameter and approximately fourteen inches in length. The effective light-sensitive area of the tube is approximately 100 times that of the usual one and one-half inch tube.

While the novel methods and structure of this invention are particularly well adapted to photoelectric tubes of large size they are also obviously applicable to tubes of small size. Moreover the tube may take a variety of shapes and be other' wise modified without departing from the spirit of the invention. AThe cylindrical form is preferred but a spherical or a toroidal shape would be suitable. These shapes are mentioned, however, merely by way of example and the lshape of the container may depart widely from any of the forms mentioned without departing from the spirit of the invention.

What is claimed is:

1. A light-sensitive device comprising an enclosing vessel having a tubular member therein, a wire helix surrounding said member, means conand a light-sensitive material on the inner side of the outer wall of said vessel. y

2. In the manufacture of light-sensitive devices the method of obtaining a coating of light-sensitive material upon the inner surface of the outer wall of the containing vessel, which method comprises depositing substantially all of the material to be used by distillation upon an auxiliary member, positioned in the vicinity of a major axis of' the vessel and well Within the vessel, heating said member by energy supplied from without said vessel and thereby revaporizing said deposit, and condensing the vapor upon the inner wall of the vessel.

3. The method of obtaining a window in a lightsensitive device of transparent material, the innersurface of the outer wall of which is coated with a layer of light-sensitive material, which method comprises heating a small area of the wall to a temperature just above the melting point of the coating material and meanwhile holding the device in such a position that the melted material will flow back upon the coating underneath.

4. The method of obtaining a window in a lightsensitive device of transparent material, the inner surface of the outer wall of which is coated with a layer of light-sensitive material which method comprises heating a small area of thewall to a temperature just above the melting point of the coating material, meanwhile holding the device in such a position that the melted material will flow back upon the coating underneath, and repeating this step for other small areas lying along a line forming the upper boundary of the window and subsequently repeating the process, progressing downwardly, until an area of the. desired size has been cleared.

5. A light-sensitive device comprising a vessel of transparent material having a hollow reentrant tubular portion out of contact with said vessel at its 'inner end, an anode around said portion throughoutlmost of its length and rigidly supported thereby, and a cathode comprising light-sensitive `material lying along a portion only of the wall `of said vessel, theremaining portion comprising a window for the admission of light to activate said cathode.

6. A light-sensitive device comprising a cylindrical vessel having a diameter of several inches and a length of at least three times the diameter, a cathode Within said vessel in the form of a layer'of light-sensitive material upon approximate- 120 ly half of the inner surface of the outer wall, -the 4 remaining portion constituting a Window for admitting light to activate said cathode, a tubular member nearly as long as said vessel extending along the major axis thereof and rigidly con- '125 nected thereto at one end only, and a wire anode wound around said tubular member and rigidly supported thereby.

7. A light-sensitive device comprising a cylindrical vessel of transparent material having a diameter of at least several inches and a length much greater than the diameter, a cathode Within said vessel in the form of a layer of light-sensitive material upon approximately half of the inner surface of the outer wall, the remaining portion constituting a window for admitting light to activate said cathode, a tubular member of transparent material within said vessel extending along its major axis, one end only of said member being supported by said vessel, and an open-work anode rigidly supported at many spaced points thereof by said tubular member. ductively connecting adjacent turns of said helix,

8. In the manufacture of light-sensitive devices the method of obtaining a coating of light-sensitive material upon the inner surface of the outer wall of the enclosing vessel for said device which comprises removing gas from the vessel, causing vapor of said material to enter said vessel in the form of a stream, causing a portion` of said vapor to condense upon the inner surface of the outerwall of said vessel, heating the outer'wa'll of said vessel and simultaneously cooling a sur-- face lying along the major-axis of said vessel and well within the vessel,whereby' substantially -all of said material is causd. to deposit upon said surface, applying heating energy from without the vessAel/to'revaporize the deposit on said surface, and condensing the vapor upon the inner surface cially cooling/said electrode well below room temperatur'ey'and simultaneously heating said deposit to cause a redeposition o! light-sensitive material on .said electrode.

' 10. A light sensitive device comprising a-tubular shaped vessel of transparent material, a cathode therein in the form of a layer of lightsensitive material lying along the curved surface of a large portion ofthe wall ofysaid vessel and substantially thefull length thereof, a window opposite said layer'of light sensitive material and of about the same dimensions as said layerto admit light to activate Vsaid cathode, a -long hollow tubular member of transparent material, within and coaxial with said vessel and secured thereto atone end and extending near to but out of contact ltherewith at vthe opposite end of -said vessel, and

a'n open-work anode rigidly supported by said tubular member, whereby said anodec is substantially uniformly spaced throughout its length from said cathode, is rigidly supported to lavoid vibration and, together with the support, oiers little obstruction tothe passage of lightfrom said window to said cathode. Y -.11Y. A light sensitive device comprising a tubular shaped vessel of transparent material having adiameter at least of the order of several inches and a lengthat least three times the diameter, a cathode therein in the form of a layer of light sensitive material lying alo/ng the curved surface o f a large portion of the wall of said vessel and substantially the full length thereof, a window opposite said-layer of said light sensitive material and of about the same dimensions as said layer 'to admit light to activate said cathode, a long hollow tubular member of transparent material within and coaxial with said vessel and secured thereto at one end and extending near to but out of Vcontact therewith at the opposite end of said vessel, said member being open at the vend which f is secured to the vessel and closed at its other end, and an open-work anode rigidly supported by said tubular member, whereby said anode is substantially uniformly spaced throughout its length from said cathode, is rigidly supported-to avoid vibration and, together with the support, of-

fers little obstruction tozthepassage of light from said window to said cathode. 1

` A12. A light sensitive device comprising a vessel and a hollow rigid anode structure of general cylindrical form and of length many times its die ameter extending within said vessel and supported at one end only thereby, and a cooperatingA cathode 'within said vessel about equally spaced throughoutv from said anode structure.

GEORGE R. STILWELL. 

